The invention relates to vacuum-driven actuators, and more particularly to the control of vacuum driven actuators.
It is known to use vacuum-driven actuators in automobiles. One example of a vacuum-driven actuator is an actuator flap of a variable intake manifold. A vacuum is built up during a throttled engine operation within the intake manifold and is generally stored in a reservoir for future actuation of the flap. A pressure equalization and a vacuum reduction take place with every activation of the actuator, but under normal driving conditions, the vacuum level rebuilds quite quickly.
However, there are driving conditions, particularly full load or the stratified charge operation of direct injection engines, under which the intake manifold vacuum may not be re-generated quickly enough to ensure sufficient switching or activation capacity. Extreme cases may result in either no actuation or incomplete actuation of the actuators. The consequences of activating a switching process in a two cylinder bank system without sufficient vacuum may include the switching of flaps in one bank while the flaps in the other bank are not switched, causing a clearly noticeable engine roughness, and apparent strong irregularities of the cylinder charge.
Rather than risking an incomplete switching as a result of an insufficient vacuum, it is desirable to detect such a condition before the activation is attempted in order to prevent incomplete switching of the actuator.
In one embodiment, the present invention provides a method of determining whether the vacuum within the vacuum reservoir is sufficient to completely execute the desired actuator movement before activating the switching process. If the available vacuum is insufficient, the switching process is disabled until enough vacuum becomes available. The method of the invention is well suited for application where no vacuum pumps are used.
The present invention also provides a method of controlling a vacuum-driven actuator in a vehicle. The method includes determining the actuator is to be actuated, determining an amount of vacuum available to actuate the actuator, and determining whether the available vacuum is sufficient to actuate the actuator. The method further includes actuating the actuator only when the available vacuum is sufficient, and preventing actuation of the actuator when the available vacuum is insufficient.
In one aspect of the invention, the vehicle includes a vacuum reservoir for storing the available vacuum, and determining the amount of vacuum available further includes determining a manifold pressure, and using the determined manifold pressure to determine a reservoir pressure. In another aspect of the invention, determining the amount of vacuum available further includes determining an amount of vacuum lost from the vacuum reservoir during a previous actuation of the actuator, and determining a new reservoir pressure based on the amount of vacuum lost. In yet another aspect of the invention, the vehicle includes a vacuum reservoir for storing the available vacuum, and determining the amount of vacuum available includes modeling the reservoir pressure.
The present invention also provides an actuator control system in a vehicle. The control system consists of a switching monitor operable to determine when the actuator is to be actuated, a vacuum level module operable to determine an amount of vacuum available to actuate the actuator, a switch operable to actuate the actuator, and a switch controller operable to determine whether the available vacuum is sufficient to actuate the actuator, and to actuate the switch only when the available vacuum is sufficient to actuate the actuator.
In one aspect of the invention, the vehicle includes a vacuum reservoir for storing the available vacuum, and the vacuum level module further includes a manifold pressure monitor operable to determine a manifold pressure, an ambient pressure monitor operable to determine an ambient pressure, and a reservoir pressure monitor operable to determine a vacuum reservoir pressure. In another aspect of the invention, the switch controller further includes a first comparator operable to find an absolute pressure difference between the ambient pressure and the reservoir vacuum pressure, and a second comparator operable to compare a pre-determined threshold and the absolute pressure difference.